1. Field of the Invention: The present invention relates to an improved device for sharpening the teeth of a chain saw and, more particularly, to a chain saw sharpener that permits the consecutive sharpening of left-hand and right-hand teeth and provides for the accurate, uniform sharpening of the chain saw teeth despite repeated use.
2. State of the Art: An assortment of portable devices are available for the on-site sharpening of the teeth of a chain saw. Such devices are typified by U.S. Pat. Nos. 4,404,871 and 3,744,349, in which the sharpening devices are secured to the cutter bar of the chain saw so as to overlie the chain and a removable burr is rotatable with respect to each device to sharpen the teeth of the chain.
Common problems accompany the use of these sharpening devices, principal among them being the inability to uniformly sharpen both the left-hand and right-hand teeth, and the repeated adjustment of the sharpening device in an attempt to so sharpen the chain saw teeth. Uniformity in the size and shape of the cutting teeth is essential for obtaining a straight, even cut through a work piece. Additionally, the devices of the above-referenced patents require a relatively involved setup procedure in which a plurality of jig members must be manipulated before a person is able to use the sharpening device. Because of the numerous adjustments required to set up their devices, the settings of the sharpening devices invariably change during use, resulting in either a constant readjustment of the devices or a non-uniform sharpening of the chain saw teeth.
In use, each sharpener described in the above-referenced patents first sharpen all the teeth of a like hand (i.e., either all the left-hand teeth or all the right-hand teeth) and then the sharpener is readjusted to sharpen the teeth of the opposite hand. This requires that the jig members be repeatedly manipulated for sharpening the teeth of opposite hands. Further, the readjustment after first sharpening all the teeth of one hand often results in an undesirable variance between the teeth of the opposite hands. An additional series of relatively complicated adjustments also must be made to cut the depth gauge portions of the teeth.
The rake angle of the teeth on different makes of saw chains often varies, the rake angle typically being 25°, 30°, or 35° with respect to a reference line perpendicular to the cutting bar of the chain saw. However, the above-mentioned devices are able to sharpen the teeth of only one rake angle, thus limiting their utility.
U.S. Pat. No. 4,677,881 is also a portable device for sharpening the teeth of a chain saw and is an improvement over prior devices. However although it allows for the sharpening the teeth of opposite hands and of different rake angle, it requires extensive machining to manufacture. This machining makes this sharpener expensive. Further to allow for the sharpening of teeth of different rake angles, an entire section of the sharpener must be removed and replaced. This adds to the cost of the sharpener and complexity of the sharpener.